1. Field of the Invention
The present invention relates to a technique capable of reducing microbubbles causing pattern defects in a method for manufacturing a semiconductor device including a photolithography process.
2. Description of the Background Art
In the method for manufacturing a semiconductor device, a resist pattern formation that is an important microfabrication process in the photolithography process is composed of sub-steps below. (1) First, a photoresist (photosensitive material) is applied to a surface of a semiconductor substrate to form a photoresist film. (2) Next, a mask is used in an ultraviolet exposure device to print a circuit pattern in the photoresist film. (3) Lastly, a development processing step of the photoresist film is performed, and the resist pattern formation is completed.
The development processing step is composed of steps below. (4) First, the photoresist film on which the circuit pattern is printed is immersed in a developing solution. (5) Next, it is immersed in a development stopping solution (rinse solution) such as pure water, and the developing solution is replaced with the rinse solution to stop development. (6) Lastly, the semiconductor substrate is rotated to disperse the rinse solution to be dried.
In step (4) of developing solution immersing process, after or while dropping the developing solution on the semiconductor substrate, the semiconductor substrate is rotated to spread the developing solution entirely on a top surface of the semiconductor substrate in many cases. At this time, air might be taken in. Moreover, the developing solution may be pressurized with nitrogen or air to drop the developing solution. Meanwhile, the nitrogen may be dissolved into the developing solution, and after the developing solution is dropped, the pressure on the developing solution decreases to the atmospheric pressure, whereby the nitrogen dissolved in the developing solution may foam. Furthermore, in a case of exposing a positive-type photoresist including a novolak resin, the nitrogen is released during a photosensitive reaction and taken into the photoresist film before development, so that it may foam when being immersed in the developing solution.
Because of the multiple factors mentioned above, when the developing solution is dropped on the surface of the photoresist film, microbubbles (bubbles) are generated in the developing solution film. Some of the microbubbles adhere to the surface of the photoresist film. The adhered microbubbles prevent the developing solution from coming in contact with the photoresist film, induce development defects, cause pattern defects, and reduce yields of the semiconductor device. Japanese Patent No. 3708433 (2005) discloses the manufacturing method that removes the microbubbles and enhances production efficiency of a semiconductor device.
The manufacturing method disclosed in Japanese Patent No. 3708433 (2005) is a method for manufacturing a semiconductor device that drops the developing solution on the semiconductor substrate and develops the photoresist film formed on the semiconductor substrate to solve the problem above. The method for manufacturing the semiconductor device includes a first step, a second step, and a third step. In the first step, the developing solution is dropped on the semiconductor substrate while making the semiconductor substrate rotate at a velocity of 100 to 500 rpm and the surface wettability of the semiconductor substrate is enhanced. In the second step, the developing solution is stopped to drop and the semiconductor substrate is rotated at a velocity of 500 to 1500 rpm. In the third step, the developing solution is dropped again while making the semiconductor substrate remain at rest or rotating it at a velocity of 100 rpm or less, and after puddling the developing solution on the semiconductor substrate, the rinse solution is dropped on the semiconductor substrate and the developing solution is washed out.
In the manufacturing method disclosed in Japanese Patent No. 3708433 (2005), the first step is capable of significantly reducing the bubbles to be generated at the time of dropping the developing solution, the second step is capable of reducing pattern defects generated because the bubbles originally existing in the developing solution remain at the same place after a lapse of predetermined time, and the third step is capable of reducing the bubbles to be generated at the time of dropping the developing solution on the semiconductor substrate.
Unfortunately, the inventors of the present invention ensures that even if the development processing steps in the manufacturing method disclosed in Japanese Patent No. 3708433 (2005) are performed, the generation of the microbubbles cannot be reduced in some cases at the time of dropping the developing solution, whereby pattern defects cannot be reduced in some cases. It is desirable to improve this point and improve yields particularly in manufacturing a silicon carbide semiconductor device in which a wafer is expensive.